Electrically conductive crown architecture for a tire of a heavy duty civil engineering vehicle

Abstract

A radial tire ( 10 ), with the sidewalls thereof ( 20 ), and the tread thereof ( 30 ) arranged for minimizing the temperature of the tire while guaranteeing its electrical conductivity. The tread ( 30 ) comprises two wings ( 311, 312 ) and a central portion ( 32 ). These components rest on a base layer ( 33 ) radially on the inside of the tread ( 30 ). The base layer ( 33 ) contains a lateral portion ( 331, 332 ) partly in contact with a tread wing ( 311, 312 ). This structure of the crown of the tire, in contact with the carcass reinforcement makes it possible to constitute a preferential conductive pathway of the electric charges between the rim and the ground when the tire is mounted on its rim and flattened on the ground.

The invention claimed is: 
     
       1. A tire for heavy vehicle of construction plant type comprising:
 a tread comprising two axial end portions or tread wings axially separated by a central portion; 
 a base layer, radially on the inside of the tread, comprising at least one lateral portion at least partly in contact with the tread wing; 
 a crown reinforcement, radially on the inside of the base layer, comprising at least one crown layer, having metallic reinforcers that are coated in an electrically-conductive elastomeric compound; 
 two sidewalls in contact at least partly with the tread wings connecting the tread wings to two beads, adapted to come into contact with a mounting rim by means of a bead layer made of electrically-conductive elastomeric compound; 
 each said sidewall being axially on the outside of a carcass reinforcement comprising at least one carcass layer having metallic reinforcers that are coated in an electrically-conductive elastomeric coating compound; 
 at least one tread wing having a first elastomeric compound M 1  having a thermal conductivity λ 1  and an electrical resistivity ρ 1 ; 
 the central tread portion having a second elastomeric compound M 2  having a viscoelastic loss tgδ 2 ; 
 the base layer having a third elastomeric compound M 3  having a thermal conductivity λ 3  and an electrical resistivity ρ 3 ; 
 each said sidewall having a fourth elastomeric compound M 4  having a viscous dynamic shear modulus G″4, 
 wherein the first elastomeric compound M 1  of at least one said tread wing has a thermal conductivity λ 1  at least equal to 0.190 W/m·K, wherein the second elastomeric compound M 2  of the central tread portion has a viscoelastic loss tgδ 2  at most equal to 0.06, wherein the third elastomeric compound M 3  of the base layer has a thermal conductivity λ 3  less than the thermal conductivity λ 1  of the first elastomeric compound M 1  of the at least one tread wing, wherein the electrical resistivities ρ 1  and ρ 3  respectively of the first elastomeric compound M 1  and of the third elastomeric compound M 3  are at most equal to 106 ′Ω·cm, so that the bead layer, the elastomeric coating compound of the carcass layer, the coating compound of the at least one crown layer, the base layer, and the tread wing constitute a preferential conductive pathway of the electric charges between the rim and the ground when the tire is mounted on its rim and flattened on the ground, and wherein the fourth elastomeric compound M 4  of each said sidewall has a viscous dynamic shear modulus G″ 4  at most equal to 0.125 MPa. 
 
     
     
       2. The tire according to  claim 1 , at least one said lateral portion of the base layer having an axial width, wherein the axial width of the lateral portion of the base layer is at least equal to 200 mm. 
     
     
       3. The tire according to either of  claim 1 , wherein the base layer is formed by two separate said lateral portions each having an axial width L 331  and L 332 . 
     
     
       4. The tire according to either of  claim 3 , wherein the base layer is formed by two separate said lateral portions, respectively formed by the same third elastomeric compound M 3 . 
     
     
       5. The tire according to one of  claim 1 , wherein the base layer is formed by two separate said lateral portions, the respective axial widths of which L 331  and L 332  are equal. 
     
     
       6. The tire according to either of  claim 1 , wherein the base layer is formed by a single portion, in continuous contact with the entire central tread portion and in contact at least partly with at least one said tread wing. 
     
     
       7. The tire according to any one of  claim 1 , wherein at least one said lateral portion of the base layer is in contact at least partly with a said tread wing over a length at least equal to 10 mm. 
     
     
       8. The tire according to any one of  claim 1 , wherein the first elastomeric compound M 1  of at least one said tread wing is an electrically-conductive rubber composition based at least on polyisoprene, on a crosslinking system and on at least one reinforcing filler comprising carbon black, having a BET surface area at least equal to 110 m 2 /g, and a content at least equal to 30 phr and at most equal to 80 phr. 
     
     
       9. The tire according to any one of  claim 1 , wherein the second elastomeric compound of the central tread portion is a rubber composition based on at least one diene elastomer, on a crosslinking system, and on a reinforcing filler comprising carbon black, having a BET surface area at most equal to 115 m 2 /g, and a content at most equal to 40 phr, and silica, at a content at most equal to 15 phr. 
     
     
       10. The tire according to any one of  claim 1 , wherein the second elastomeric compound of the central tread portion is a rubber composition based on at least one diene elastomer, on a crosslinking system, and on a reinforcing filler, at an overall content at most equal to 40 phr, and comprising carbon black, and silica. 
     
     
       11. The tire according to any one of  claim 1 , wherein the second elastomeric compound M 2  of the central tread portion is an electrically-conductive rubber composition based on at least one diene elastomer, on a crosslinking system, and on a reinforcing filler comprising carbon black, having a BET surface area at least equal to 120 m 2 /g, and a content at least equal to 35 phr and at most equal to 80 phr, and silica, at a content at most equal to 15 phr. 
     
     
       12. The tire according to any one of  claim 1 , wherein the third elastomeric compound M 3  of the base layer of the tread is an electrically-conductive rubber composition based at least on polystirene, on a crosslinking system, and on at least one reinforcing filler comprising carbon black, having a BET surface area at least equal to 110 m 2 /g, and a content at least equal to 30 phr and at most equal to 80 phr. 
     
     
       13. The tire according to any one of  claim 1 , wherein the elastomeric compound of each sidewall has a rubber composition based on at least one blend of polyisoprene, natural rubber or synthetic polyisoprene, and polybutadiene, on a crosslinking system, and on a reinforcing filler, at an overall content at most equal to 45 phr, and comprising carbon black, at a content at most equal to 5 phr, and, predominantly, silica, at a content at least equal to 20 phr and at most equal to 40 phr.